THE PALIMPSEST LANDSCAPE IN NEW ZEALAND; MULTIPLE GLACIER ADVANCES OF DECREASING MAGNITUDE (Invited Presentation)

South Island, New Zealand, contains one of the most comprehensive records of Quaternary glaciation which is especially valuable from a globally important climatic region. In some locations, a full suite of glacial landforms and sediments, from the neoglacial through to the late Pleistocene, are spectacularly well-preserved giving rare insight into ice-marginal process-form regimes and their paleo-glaciological implications. This invited talk will highlight how stratigraphic logging and luminescence dating of buried stratigraphy, not expressed as landforms, has revolutionised the way we perceive the sediment-landform imprint of New Zealand’s glacial system. New sedimentological evidence from outcrops at Lake Tekapo records phases of valley aggradation throughout multiple glacial cycles which is preserved in substantial volumes. Luminescence dating reveals that the sediments do not relate to the age of the landforms stratigraphically above them and suggests that recent glacial advances lacked capacity to erode the underlying pre-existing sediments deposited during the penultimate glacial cycle, thereby reducing the accommodation space in the valley overdeepening. These results support increasing evidence from similar valley fills across South Island that were not deposited in association with the last major ice advance, nor indeed the last glacial cycle, as typically expected. Such findings are not new features of the Quaternary stratigraphy in New Zealand; extensive in-situ sediments that have survived subsequent ice re-advances are also recognised from terraced outwash surfaces in the upper Clutha, central Otago, together with records from the Takaka valley in northwest Nelson, the Cascade Plateau in Fiordland, and across north Canterbury in the Hope, Rakaia and Rangitata river valleys. Overall, whilst moraine sequences reveal ice was more extensive during previous glaciations, the sediment sequences associated with them reveal that deposition was considerably more voluminous than more recent glacial advances. It is apparent, therefore that South Island, New Zealand, showcases not just remnants of Quaternary-age strata but high-quality outcrops containing valuable archives of glacial history and climatic change, as well as seismic and tectonic activity over millennia.